Concept for actually making VIN useful - "MBC-5B"

Discussion of programming and development for the original Game Boy and Game Boy Color.
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kevtris
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Re: Concept for actually making VIN useful - "MBC-5B"

Post by kevtris » Thu Jun 22, 2017 8:46 pm

ImATrackMan wrote:[OLDER IMAGE]
Did some of the changes, namely went to an OSC, added the decoupling cap, and the resistor from VIN to ground. I also did a little rewiring but I don't think it made much difference. The width of the power traces was fine since I used .5mm (19.86 mils)
kevtris wrote:I suggest a 1uf between the output and the GB input for starters.
I forgot to ask if that was before or after the resistor. I assume after.
Yep after, just like that. looks a lot better. Make sure pin 1 of that oscillator isn't an enable input or anything. if it's NC I suggest connecting it to VCC because it's a positive output enable on a lot of models, but check the data sheets to be sure.
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ImATrackMan
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Re: Concept for actually making VIN useful - "MBC-5B"

Post by ImATrackMan » Fri Jun 23, 2017 1:05 am

kevtris wrote:Yep after, just like that. looks a lot better. Make sure pin 1 of that oscillator isn't an enable input or anything. if it's NC I suggest connecting it to VCC because it's a positive output enable on a lot of models, but check the data sheets to be sure.
Okie dokie. I'll make the minor change of hooking it up to VCC, though the datasheet says it doesn't really need it because of an internal pullup. I made a major change to the design to remap the YMZ to $4400 and $4401 at the request of nitro2k01. A0 is now actually A0, and the 138's been wired from A10 to A15 so I hope that's right. I also made the minor addition of two spots to wire up some pots for bias/gain control, again at the request of nitro2k01. If everything's all clear, I'll order all the parts and boards when I'm next free.
Image
EDIT: And I just realized I connected Y0 to /CS instead of Y1. I keep forgetting the first pin is VCC and not an output pin.
Last edited by ImATrackMan on Fri Jun 23, 2017 2:16 am, edited 1 time in total.

lidnariq
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Re: Concept for actually making VIN useful - "MBC-5B"

Post by lidnariq » Fri Jun 23, 2017 1:24 am

... But if you put the registers at $4400-$47FF, that'll overlap with the MBC register at $4000-$5FFF...

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ImATrackMan
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Re: Concept for actually making VIN useful - "MBC-5B"

Post by ImATrackMan » Fri Jun 23, 2017 2:12 am

lidnariq wrote:... But if you put the registers at $4400-$47FF, that'll overlap with the MBC register at $4000-$5FFF...
According to Nitro:
Writes to areas like 6000 could conflict with for example EMS's multi ROM functionality. I might personally put it in a MBC register space which has a well defined use, but where writing to it doesn't produce negative results. For example SRAM bank.

For example... 5-6 address bits would be enough to put it in the $48xx area. This would make writes to the sound chip safe (would only change the SRAM bank
which doesn't really matter) whereas actual SRAM bank select writes could be done to $4000
Me: [but] what sort of problems would this cause on the EMS multirom? If anything it seems like you'll just be sending the YMZ garbage
which would immediately stop as soon as you choose a game.
The problem is the reverse. If you're trying to to write to the YMZ, the EMS might think it's a multi ROM request and map out the currently running ROM. Boom crash!
He then told me how to wire the 138 for $4400, I just followed the advice of someone much more experienced than I am.

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Jeroen
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Re: Concept for actually making VIN useful - "MBC-5B"

Post by Jeroen » Fri Jun 23, 2017 5:38 am

ImATrackMan wrote: EDIT: And I just realized I connected Y0 to /CS instead of Y1. I keep forgetting the first pin is VCC and not an output pin.
If you are, ignore this comment. But if you're not using schematic capture to wire everything up first, I strongly recommend doing that on future projects. It'll help prevent silly mistakes.

nitro2k01
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Re: Concept for actually making VIN useful - "MBC-5B"

Post by nitro2k01 » Sat Jun 24, 2017 11:25 pm

lidnariq wrote:... But if you put the registers at $4400-$47FF, that'll overlap with the MBC register at $4000-$5FFF...
That is intentional. The point is to avoid for example $6000-$7FFF which may have different functionality on different flashcarts precisely because it's mostly unused otherwise. $4000-$4FFF on the other hand has a behavior that's both predictable between various cart hardware and mostly non-destructive. Yes, the SRAM bank register will be changed by writing to $4400, but this can easily be restored by writing the desired bank value to $4000 which will also not affect the sound chip.

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Re: Concept for actually making VIN useful - "MBC-5B"

Post by tepples » Sun Jun 25, 2017 7:58 am

Doesn't the SRAM bank register also affect the ROM bank on some MBCs?

nitro2k01
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Re: Concept for actually making VIN useful - "MBC-5B"

Post by nitro2k01 » Sun Jun 25, 2017 9:53 am

tepples wrote:Doesn't the SRAM bank register also affect the ROM bank on some MBCs?
It does, on MBC1. But again, this is still predictable behavior that can be easily recovered.

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ImATrackMan
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Re: Concept for actually making VIN useful - "MBC-5B"

Post by ImATrackMan » Mon Jun 26, 2017 1:18 am

I went ahead and got 10 boards and ordered the parts for five. If they work 100%, or reasonably well, I'll buy the parts to populate the other five boards and send them out to whoever wants to write something or just play around with them.

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